Mind the balloon


By: Dorri Mang and Marieke Scherjon

Balloons for children seem rather innocent, but in Madrid they are not allowed in the subway since one metallic balloon broke down the complete underground system.

After walking down several flights of stairs to line 6 in the city center of Madrid, you may be shocked to see quite a few signs, which look large, intimidating and even threatening, and leading us to believe that there is something funny going on in Madrid. Confusing to visitors, a norm to residents, and a stark reminder of a childish mistake for a certain little Madrileño. That’s right. Whenever entering the subway stations, the first thing that welcomes you is a cacophony of large, daunting stop signs, telling you to not bring … guns? bombs? alcohol? Nope. Balloons.

In Madrid, helium-filled foil balloons, or metallic balloons, are denounced as a hazard to public safety. In other words, don’t take the metro if you’re bringing home decorations to set up for your child’s birthday party. The seemingly innocent children’s balloon can mark you as a subject of inciting public unrest.

Luciana Abrejo (43) of the Madrid railway service explains the reasoning behind the ban. “I remember coming into work last year, I believe it was December 2, 2015. It started out as a semi normal day, but then a child accidentally let go of his metallic balloon in the Sol Station where I was working. The balloon floated through Line 2, and got stuck on the overhead power cable, and touched an incoming train. This created a ‘traction jump’, which is a shock similar to a fuse blowing, and caused the trains to be stopped in Madrid for an hour. It was a turning point. Since then, we have had the signs up in the station. Now, they will be up forever.”

The physical explanation is that as helium balloons are filled with gas, they rise up when you let them go, which in and of itself is not a big deal. However, power cables that run over the roof of the subway system generate the power for the metro. If a helium balloon were to touch it, it will short circuit, and could result in a power outage, sparks, or even a minor explosion, leaving trains to stall and cause massive delays.

You can see similar signs in other metro lines around the world with similar subway systems: Schiphol Airport in Amsterdam, or in Hong Kong.

For now, the citizens of Madrid should obey the signs and understand the message. By all means, bring your alcohol, guns, and bombs to the subway. But leave your balloons at home.